1. Field of the Invention
The present invention relates to a circuit for controlling the audio signal output of a television in which there is made a decision as to whether video and audio signals are input from an external signal source, and then the audio output signals are properly controlled according to whether the input audio signal is of a mono or stereo-type.
2. Description of the Prior Art
Generally, a television receiver either receive a signal from transmitted radio waves coupled through an antenna, or else receives video signals and the like from other signal sources in order to process them. That is, a television receiver can receive audio and video signals from a video cassette recorder (VCR) to display the video pictures on a screen, and outputs the audio signals through speakers to produce sound. In this case, the received audio signal may be a mono-type signal in which case the signal is supplied to only one of the left and right channels, or the signal may be a stereo-type signal in which the audio signal is supplied to both of the left and right channels.
In the case of a stereo-type signal, the audio signal which has been input into the respective left and right side channels is properly output through the speakers and thus, there is no problem. However, in the case of a mono-type signal in which the audio signal is supplied to only one of the two channels, the sound is output through only one speaker.
In an attempt to overcome the above-described difficulty of only outputting the sound through one speaker, as shown in FIG. 1, the conventional circuit for controlling the audio signal output of a television is configured such that the user must manipulate a mono/stereo selecting switch on the television. Thus, the audio signal which is input into one of the channels is manipulated to be supplied to both of the channels, so that the sound is output through both the left and right speakers, just as with a stereo-type signal.
Referring to FIG. 1, audio signals which are supplied from an external source, such as from a video cassette recorder, are input into first and second terminals 1 and 2. Then, the signals are supplied through capacitors C1 and C2 to an audio/video (A/V) switch 100.
The signals are processed by the A/V switch 100, and then the audio signals corresponding to the left and right channels are output through an amplifier (not shown) to a speaker (also not shown). A mono/stereo switch SW1, which when closed connects the first and second terminals, has the effect of connecting the left and right channel circuits.
The conventional audio signal control circuit as described above, operates in the following manner. If the audio signal which has been supplied from an external source is a stereo-type signal, then the user turns off switch SW1 so that the audio signals corresponding to the right and left channels and input into the first and second terminals are supplied to the A/V switch 100.
On the other hand, if the audio signal from an external source is a mono-type signal, then, the user turns on the switch SW1, so that the audio signal supplied to only one of the left and right channels, i.e., the first and second terminals, passes through both of the left and right channels and is supplied to the speakers, thereby producing a quasi-stereo sound.
However, in the conventional audio signal control circuit, there is the problem that the user must manually manipulate the switch.
Efforts to overcome this problem have been ceaselessly attempted. One example of these attempts is disclosed in U.S. Pat. No. 5,187,576. Here, pilot signals are employed to determine whether or not the audio signals are mono or stereo-type signals, and accordingly the user optionally switches over to a stereo-mode.
However, this technique also requires a user to select the type of sound to output, and is rather complicated.